A key intermediate in the production of nylon is adiponitrile (ADN). ADN is commercially produced via hydrocyanation of 1,3-butadiene and 3-pentenenitrile (3PN) in the presence of a catalyst including nickel(0) and phosphite ligand. The phosphite ligand used commercially is a monodentate phosphite, such as a triarylphosphite, that forms nickel-ligand complexes serving as catalyst precursors for the reactions. Although useful, monodentate phosphites can result in relatively low catalyst activity and relatively high nickel consumption.
Recently, significant improvements in nickel catalyst activity and yield to 3PN and ADN have been realized by using catalysts including nickel(0) and bidentate phosphites as ligands. Bidentate phosphite ligands, in general, contain two phosphorus donor atoms that can form cyclic chelate structures with a single transition metal.
Bidentate phosphites of the general structure (RO)2P(OZO)P(OR)2, also referred to as diphosphites herein, are of special interest. Traditionally, such diphosphites can be synthesized by preparing a phosphorochloridite, (RO)2PCl, from the reaction of PCl3 with ROH in the presence of a tertiary organic amine. Then in a subsequent reaction, a difunctional alcohol, such as HO—Z—OH, can react with the phosphorochloridite in the presence of additional tertiary organic amine, giving (RO)2P(OZO)P(OR)2. The tertiary organic amine can neutralize the HCl co-product in both reaction steps through the formation of a tertiary organic amine hydrogen chloride salt. The nature of the ROH and the HO—Z—OH as well as the conditions chosen for each reaction step can influence the selectivity to the desired products.
U.S. Pat. No. 5,235,113 and WO 96/22968, for example, disclose the synthesis of diphosphites. U.S. Pat. No. 5,235,113 discloses a process for the preparation of a diphosphite of structure (RO)2P(OAO)P(OR)2 where A is biphenyl and R is 3,6-di-t-butyl-2-naphthyl. WO 96/22968 discloses syntheses of multidentate phosphite compounds of the type (ArO)2P(OZO)P(OAr)2, where Ar and Z are substituted or unsubstituted aryl groups.
U.S. Pat. No. 6,069,267 provides a process for the preparation of organodiphosphites of the general formula (R1O)2P(OZO)P(OR1)2, wherein R1 and Z are different substituted or unsubstituted aryl groups
WO 2004/050588 discloses that low temperature and viscosity of the product mixture below 0° C., for example between 0° C. and −20° C., add significantly to operating cost and process complexity.
WO 2004/091780 also describes a process for preparing a crude ligand mixture including bidentate phosphite ligands of the structural formula (R1O)2P(OZO)P(OR1)2 by contacting a first reaction product including (R1O)2PCl at a temperature between about −25° C. and about +35° C. with about one half molar equivalent of HO—Z—OH in the presence of an organic base.
WO 2010/123743 and WO 2010/123747 describe examples of methods for making organodiphosphites.